Magnetron tube



R. W. WOLFE MAGNETRON TUBE May 1, 1962 2 Sheets-Sheet 1 Filed July 18, 1960 States This invention relates to magnetron-type electron discharge tubes and to improvements in the construction of such tubes, particularly in the portion thereof which provides the required magnetic field.

This application is a continuation-in-part of application Serial No. 861,114, filed December 21, 1959, which is now abandoned.

One form of magnetron tube, to which the principles of the invention apply, includes an electrode assembly which comprises an elongated central cathode and a pluraltiy of groups of elongated electrodes surrounding the cathode and secured together at their opposite ends by means of insulating end disks or plates. All of the electrodes are substantially parallel to each other. An external cylindrical magnet surrounds the tube envelope and electrode assembly and provides a longitudinal magnetic field within the tube. While these beam switching tubes are quite satisfactory, they have features which, under some circumstances, may be considered drawbacks. For example, by some standards, due to the external magnet, the tubes are considered undesirably large and heavy; and this problem of size and weight is further complicated when the tubes are provided with external magnetic shields.

Accordingly, the principles and objects of the present invention are concerned with the provision of an improved miniaturized magnetron tube having improved means for providing a magnetic field.

In brief, a magnetron tube embodying the invention includes an electrode assembly in which electron flow is controlled by means of crossed electric and magnetic fields therein. A pair of disk-shaped magnets are provided spaced apart to provide a magnetic field between them and the disk magnets are oriented in operative relation with the electrode cage so that the magneticfield between them becomes the magnetic field required for the electrode cage. Efficient shielding may be achieved, if desired, by means of a simple, thin sheet of metal foil surrounding the magnet disks and electrode assembly.

The invention is described in greater detail by reference to the drawing wherein:

FIG. 1 is a perspective view, partly in section, of a magnetron beam switching tube embodying the invention;

FIG. 2 is a sectional view of the tube of FIG. 1 showing the electrode assembly thereof;

FIG. 3 is an elevational view of a portion of the tube of FIG. 1 on a slightly smaller scale;

FIG. 4 is an elevational view of a modification of a portion of the tube of FIG. 2;

, FIG. 5 is a sectional elevational view of a modification of the invention;

FIG. 6 is a sectional elevational view of another modifiaction of the invention; a

FIG. 7 is a sectional view along the lines 77 in FIG. 6; and

FIG. 8 is a sectional elevational View of another modification of the invention.

The principles of the invention are particularly applicable to a magnetron beam switching tube such as the type 6700 tube. This type of tube 10, referring in FIG. 1, includes an envelope 12 having a base or stem 14 in which a plurality of tube contact pins 15 are sealed. The envelope contains an electrode assembly atom "ice

or electrode cage 16 comprising a central longitudinally elongated cathode 17 and a plurality of groups of electrodes spaced radially equidistantly from the cathode and surrounding the cathode. The tube electrodes are parallel to each other and to the cathode.

Each group of electrodes includes an elongated spade electrode 18 which is generally U-shaped and is the closest electrode to the cathode. Each group of electrodes also includes a generally L-shaped target electrode 19 which, effectively, occupies the space between two adjacent spades. Each spade electrode serves to form and hold an electron beam on its associated target electrode which provides an output signal therefrom. A generally rod-like switching electrode 20 is also included in each group of electrode and is positioned between each target electrode and the adjacent spade electrode. The switching electrodes are known as switching grids and may be used to switch an electron beam from one group of electrodes to the next.

The electrodes of the assembly 16 are secured together by means of top and bottom insulating end disks 22 and 24 of mica or the like which have facing surfaces 26 and 28 and outer surfaces 30 and 32, respectively. The mica disks are provided with suitable apertures 34 (bottom) and 36 (top) which receive and secure lower end tabs or portions 38 and upper end tabs or portions 40 of the various tube electrodes in a manner well known in the art. The various electrodes are electrically connected to the tube pins 15 by means of metal wires 50 suitably secured to the lower electrode end tabs 38, as described below.

The tube 10 also includes magnet means, to be described, to provide a longitudinal magnetic field in the tube which cooperates with electric fields therein to provide the desired electron flow. According to the invention, the means for providing the desired longitudinal magnetic field in the electrode cage 16 comprises a topdisk-shaped permanent magnet 52 having top and bottom surfaces 54 and 56 (FIG. 3), and a bottom diskshaped permanent magnet 58 having top and bottom surfaces 60 and 62 (FIG. 3). The disk magnets are spaced apart with their poles oriented as shown so that the facing surfaces 56 and 60 of the magnets are of opposite polarity. Thus, the desired magnetic field flow between the magnets. The magnets thus spaced apart are positioned at opposite ends of the electrode cage so that the magnetic field between them provides the required longitudinal magnetic field in the tube 10. Thus, the disks are oriented so that they lie transverse to the longitudinal axis of the electrode cage 16. The magnet disks have sufficient area so that they cover at least the radial distance between the cathode and the spade electrodes. Thus, a favorable longitudinal magnetic field is provided in the critical region of current flow between the cathode and the spade electrodes.

The magnet disks 52 and 58 may be mounted and secured within the tube envelope in many different ways. In one arrangement shown in FIG. 1, a plurality of elongated metal support rods 64 are oriented parallel to and spaced from the tube electrodes and are mounted in suitable apertures in the peripheries of the top and bottom mica disks 22 and 24. The support rods are of sufiicient length so that their upper ends 66 extend above the top mica disk, and their lower ends 68 extend below the bottom disk. The rods 64 are secured to the top disk by means of metal locking tabs 70 welded or otherwise secured to the rods at such a location that they bear against the lower surface 26 of the mica disk 22. Similar tabs 72 are secured to the rods in contact with the upper surface 30 of the mica disk 22. The tabs 72 are preferably of such a height that they extend above the upper ends of the electrodes and above the electrode tabs 40 3 which are inserted through the apertures 36 in the top mica disk 22. Similarly, the support rods 64 are secured to the bottom mica disk 24 by means of tabs 74- secured thereto in contact with the upper surface 23 of the disk and tabs 76 secured thereto in contact with the lower surface 32 of the disk. Again, the tabs 76 are of sufiicient height so that they extend below the lower ends of ll electrodes and below the tabs 38 of the electrodes. All of the tabs which secure the rods 64 in position are insulated from all of the electrodes of the electrode assembly 16.

The top magnet disk 52 is provided with suitable peripheral apertures by means of which it is threaded on the upper ends 66 of the rods 64. The disk 52 rests on the tabs 72 and is locked in position by means of tabs 80 secured to the support rods in contact with the upper surface 54 of the magnet disk 52. The bottom magnet disk 58 is similarly provided with suitable apertures by means of which it is threaded on the lower ends 68 of the support rods with its top surface 60 in contact with the tabs 76. The magnet disk 58 is locked in position by means of tabs 84 secured to the rods in contact with the lower surface 62 thereof.

The entire electrode assembly 16 may be supported in the envelope 12 by securing the lower ends 68 of the support rods 64 directly to selected tube pins 15 as shown or by means of intermediate connecting links.

The disk magnets 52 and 58 are thus secured in position, spaced from the electrode tabs 38 and 40 and other electrode parts. This is a necessary arrangement if the magnets are not made of insulating material. In addition, if the magnets are not electrical insulators, it is necessary that the electrode leads 50 be suitably arranged so that they do not contact the lower disk 58. In one arrangement shown in FIG. 4, the electrode leads 50 extend radially from their corresponding electrode tabs, bend around the bottom magnet, and then extend radially inwardly to the appropriate tube pin 15 without touching the magnet disk. Alternatively, the electrode leads 50 may be coated with a suitable insulating material such as glass or the like and passed through apertures in the disk to the appropriate tube pins.

If the disk magnets are made of, for example, a ceramic magnetic material which has the properties of an electrical insulator, then the leads may be uninsulated andthreaded through the suitable apertures provided in the lower disk.

If desired, and if the magnet disks have suitable insulating properties, they may be used in place of the mica disks 22 and 24 to provide support for the electrodes of the electrode assembly while, at the same time, providing the required magnetic field.

One advantage of the present invention lies in the fact that the tube may be easily shielded so that tubes may be operated in close proximity to each other. Thus, a satisfactory shield 10 for the tube 10 may comprise a thin sheet of magnetic material having low reluctance and high permeability and secured in position surrounding the electrode assembly in any suitable fashion, for example, by means of a chemical adhesive or mechanical clamp or the like. The shield provides a return flow path for magnetic flux, and thus serves to reduce flux loss. This reduction in flux loss, in effect, enhances the magnetic field in the tube and allows the use of smaller magnets than might otherwise be used. If desired, the shield may comprise the entire tube envelope and the usual glass envelope may be omitted.

One form of tube, according to the invention which eliminates the usual glass envelope is shown in FIG. 5 as tube 100. This tube includes, as the greater portion of its envelope, a hollow metal cylinder 102. The material used for the cylinder is preferably one which has high magnetic permeability such as soft iron. However, since, generally, the magnetic field of a ferrite magnet weakens with increased temperature, it is desirable to use a material for the envelope the permeability of which decreases with increased temperature, Thus, a compensating arrangement is provided. One suitable material of this type is sold by the Carpenter Steel Company as Carpenter Temperature Compensator 32, Type I.

The cylinder 102 includes an upper open end which is closed by a permanent magnet disk 104 similar to magnet disk 52 of FIG. 1. The cylinder 102 is sealed to the magnet 104 according to well-known techniques. The envelope cylinder 102 also has an open lower end which is closed by a permanent magnet disk 106 similar to magnet disk 58 of FIG. 1. The magnet disk 106 comprises the base or header for the envelope 102, and tube contact pins 108 are sealed therein and suitably insulated therefrom by means of glass seals 110 or the like. The tube electrode assembly, which is schematically represented by numeral 111 and includes the same elements as the assembly 16 of FIG. 1, is suitably supported on the pins 108 and the header magnet 106.

A modification of the tube of FIG. 5 is shown in FIGS. 6 and 7 as tube 112 which includes the metal envelope cylinder 102, the top magnet 104' and bottom magnet 106. In the tube 112, the magnetic path between the magnet disks and the cylinder 102 is interrupted by means of spacer rings 114 and 116 of glass or a metal having low magnetic permeability and suitably sealed to the magnets and the cylinder. In the tube 112, the tube pins 108 may be sealed in the ring 114 (FIG. 7), rather than in the bottom magnet disk 106'. The construction of tube 112 provides a shaped magnetic field as shown by dash lines 117 which is weaker in the center of the electrode assembly than at the ends. Such a magnetic field configuration appears to aid electron flow and control.

In still another modification of the tube of FIG. 5, referring to FIG. 8, a tube 118 includes a generally elongated cup-shaped metal envelope 120 having an upper end wall 122 and an open end in which a header 124 is sealed. The header 124 comprises a plate of the same metal as the envelope 120 having tube pins 108 suitably sealed therein by means of glass seals or the like. In the tube 118, the bottom magnet disk 106" is secured to the inner surface 126 of the header 124, and the top magnet 104" is secured to the inner surface 128 of end wall 122 with the electrode assembly 111 between them.

What is claimed is:

'1. A multi-position magnetron beam switching tube of the type employing crossed electric and magnetic fields comprising an electrode assembly including a central electron-emitting cathode and a plurality of groups of electrodes arrayed about said cathode, said cathode producing an electron beam which is adapted to flow outwardly therefrom toward said groups of electrodes, and a diskshaped permanent magnet positioned at each end of said electrode assembly and providing a longitudinal magnetic field therefor, said magnets having a surface area of will-- cient extent to cover the region of current flow between said cathode and said groups of electrodes.

2. The tube defined in claim 1 wherein said disk magnets are oriented transverse to the central axis of said electrode assembly.

3. The tube defined in claim 1 wherein the ends of the electrodes of the electrode assembly are secured to said disk magnets.

4. The tube defined in claim 1 wherein the tube electrodes are oriented parallel to each other and the electrode assembly has an axis, said electrode assembly having two ends defined by the ends of said electrodes, and a diskshaped permanent magnet positioned at the ends of said electrode assembly.

5. A multi-position magnetron beam switching tube including an electrode cage in which radial electron fiow from an axial region is provided, and a pair of disk-shaped magnets positioned at the ends of said cage and providing a longitudinal field therein, the magnets having sufficient area to cover the area of electron flow in said electrode cage.

6. The tube defined in claim 5 and including a magnetic flux-absorbing shield surrounding said electrode cage.

7. A magnetron beam switching tube of the type employing crossed electric and magnetic fields having an electrode assembly including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its associated target electrode, and a switching electrode which serves to switch an electron beam from one group of electrodes to the next; said groups of electrodes being arrayed about said cathode as an axis; said electrode assembly having upper and lower ends; and a disk-shaped permanent magnet at each end of said electrode assembly and providing a longitudinal magnetic field.

8. The tube defined in claim 7 wherein said disk magnets are oriented transverse to the longitudinal axis of the electrode assembly.

9. A magnetron beam switching tube including an electrode assembly having an axially elongated configuration and including a central cathode and a plurality of groups of electrodes surrounding the cathode, said cathode being adapted to provide a beam of electrons which flows to said groups of electrodes, a permanent magnet positioned at the ends of said electrode assembly and providing a longitudinal magnetic field therein, said permanent magnets overlying the region of current flow between said cathode and said groups of electrodes, and a generally cylindrical metallic shield surrounding said electrode assembly and comprising, in combination with said magnets, the envelope for said tube.

10. The tube defined in claim 9 wherein the permanent magnet at the lower end of said electrode assembly cornprises the header for said tube.

11. The tube defined in claim 9 and including means for interrupting the conductive path between said metallic shield and said magnets, said means comprising a ring of material magnetically difierent from said shield and said magnets.

References Cited in the file of this patent UNITED STATES PATENTS 2,543,702 Mulder et a1. Feb. 27, 1951 2,721,955 Fan et a1. Oct. 25, 1955 2,876,376 Rienks Mar. 3, 1959 

